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가스분무한 Al-8wt.%Fe 합금분말의 급속응고과정에 대한 수치해석
김성균,최회진,나형용 ( Seong Gyoon Kim,Hoi Jin Choi,Hyung Yong Ra ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.5
N/A A numerical analysis on the microstructural evolutions of microcellular and cellular α -aluminum phase in the gas-atomized Al-8wt. pct droplets was represented. The 2-dimensional non-Newtonian heat transfer and the dendritic growth theory in the undercooled melt were combined under the assumptions of a point nucleation on droplet surface and the macroscopically smooth solid-liquid interface enveloping the cell tips. It reproduced the main characteristic features of the reported microstructures quite well. It predicted a considerable volume fraction of segregation-free region in a droplet smaller than l0㎛ if an initial undercooling larger than 100K is given. The volume fractions of the microcellular region(g_A) and the sum of the microcellular and cellular region(g_a) were predicted as functions of the heat transfer coefficient, h and initial undercooling, ΔT. It was shown that g_A and g_a, in the typical gas-atomization processes with h=0.1-1.0W/㎠K, are dominated by ΔT and h, respectively, but for h larger than 4.0W/㎠K, a fully microcellular structure can be obtained irrespective of the initial undercooling.
Marforming 處理한 Fe-30% Ni-0.24%C Martensite의 Tempering 擧動
金學信,金炳日,崔會珍 전북대학교 공업기술연구소 1985 工學硏究 Vol.16 No.-
The tempering behavior of marformed martensite in Fe-30% Ni -0.24%C alloy was examined by means of hardness, yield strength, ultimate tensile strength, optical microscopy and transmission electron microsco-py. The results obtained in this work are as follows ; (1) The morphology of virgin martensite at room temperature was plate martensite of transformation twin in Fe-30% Ni-0.24%C alloy. (2) The strength of Fe-30% Ni-0.24%C alloy by marforming treatment was increased due to the work hardening induced from the dislocation density increased during deformation, the formation of dislocation atmosphere induced from interaction between dislocation cell produced during deformation and solute car-bon and the stress concentration induced from crossing of twins. (3) The optical microstructures of marformed martensite tempered below 200℃ was not noticed obvious differents but aboce 300℃, precipitates of carbide were promoted as deformation degree is greater. (4) From tempered structure of virgin martensite the carbide was precipitated in the twin boundary, while the carbide from marformed martensite was precipitated in the twin boundary, cell-like structure and grain boundary of martensite plate in marformed martensite. (5) Virgin martensite and marformed martensite were attained the highest hardness, yield strength and ultimate tensile strength on tempering at 100℃ andd above 100℃, marformed martensite showed a greater softening resistance on tempering because of the effect to degress the precipitation of ε-carbide induced from interaction between interstitial carbon atom and dense dislocation and dispersion strengthening effect precipitated in dense dislocation